1. Field of the Invention
The invention relates to a polyphase linear motor with a stationary series of coils set upon an internal flux-conducting member, with a secondary excited by permanent magnetism and concentrically enveloping some of the coils, and with external ferromagnetic flux-conducting members concentrically enclosing the secondary. The invention finds application in e.g., peripheral data-processing equipment.
2. Description of the Prior Art
A polyphase linear motor of this type is described commonly owned U.S. Pat. No. 4,220,899. The entire disclosure of that patent is incorporated herein by reference.
In this reference the coil arrangement consists of at least two coils longitudinally offset relative to each other along the longitudinal motor axis, while the secondary (which is excited by permanent magnetism) is provided with a plurality of juxtaposed magnets which alternate in directions of magnetization. Spacing of the coils and spacing of the magnets along the longitudinal motor axis is matched in such a manner that cyclical energizing of the coils may generate a motive force acting upon the permanently magnetized secondary.
In the reference, the secondary supports radially magnetized magnetic plates of polygonal form, which form is preferably hexagonal. Particularly in this arrangement, several polygonal or, respectively, circular, magnet units with radially alternating directions of magnetization are axially juxtaposed. Although this construction is highly efficient, and although only a low iron weight is required since the ferromagnetic parts do not tend to saturate, construction of the secondary is a relatively expensive proposition.
In this reference a massive ferromagnetic rod forms the internal flux-conducting member. The motor is robust and simple.
In practice, however, it has been found that undesirable eddy currents, may occur in the internal flux-conducting member when the coils are energized. This decreases motor efficiency.